Studies are proposed on the regulation of several genes with posited early functions in the embryogenesis of the sea urchin, based on their production of peak amounts of RNA in early development, and late functions based on the late stage accumulation of their RNAs. Two of these genes produce different RNA forms in early and late stages: One gene switches between polymorphic forms, producing a single poly(A)+ mRNA in the early stages and two different sizes of poly(A)- mRNA in the late stages. The other switches between single early poly(A)+ and late poly(A)- mRNAs. Animalizing agents tend to increase and prolong the syntheses of early function mRNAs and delay the onset of late function mRNA synthesis. Vegetalizing agents tend to enhance late function mRNA synthesis. Two mRNA species fulfilling the criterion of early stage function are also induced to be synthesized by treatment of late stage embryos with the animalizing agent zinc sulfate. One of these induced mRNAs is the poly(A)+ form of the set of polymorphic mRNAs, described above. The induction reverses the normal developmental program of changes. To understand the mechanisms through which these developmental changes are effected and their relationship to the determinative events of embryogenesis, we shall analyze the structures of these various genes, especially to assign origins to the polymorphic mRNAs, and to study the transcription, processing and stability of the various RNAs, as well as their properties as templates for translation, to explain the functional significance of the different sizes and states of polyadenylation. The induction phenomenon will be utilized as a way of experimentally controlling gene activity. At present, two species of mRNA are known to be enriched in ectoderm tissue of the pluteus and one species in the mesoderm-endoderm tissue. We shall study the developmental enhancement of nuclear RNA compared to mRNA that appears to be involved in establishing the tissue specificity of these mRNAs. Shifts in the concentrations of all of these mRNAs in association with imbalances in the development of the three germ tissues, studied in animalized and vegetalized embryos, may be a basis for understanding the promotion of cellular differentiation by differential gene activity. These processes may pivotally decide the course of normal vs. abnormal cellular differentiation.